| Chlorine disinfection of secondary wastewater effluent and drinking water can result in the production of the potent carcinogen N-nitrosodimethylamine (NDMA) at concentrations of approximately 100 and 10 parts per trillion (ng/L), respectively. Currently, expensive ultraviolet treatment systems frequently are used in water recycling programs to remove NDMA from water that has not been subjected to conventional wastewater treatment and reverse osmosis. This research explores methods for preventing the formation of NDMA during wastewater chlorination to minimize potential human health risks and to avoid the need for expensive ultraviolet treatment.; Laboratory experiments indicate that NDMA formation can occur when monochloramine reacts with dimethylamine. NDMA is also produced when hypochlorite or hypochlorous acid reacts with dimethylamine.; To quantify and characterize the organic nitrogen precursors of NDMA and to delineate their fate during wastewater treatment, analytical techniques were devised for dimethylamine and for the family of NDMA precursors. Precursors associated with solids were related to the return to the main waste stream of water containing certain cationic polyacrylamide polymers from sludge thickening operations. Dissolved precursors, consisting of dimethylamine and tertiary amines with dimethylamine functional groups, were most likely derived from municipal sources.; Biological treatment effectively removed dimethylamine, reducing its concentration by over 95% during secondary treatment. After secondary treatment, dimethylamine only accounted for approximately 10% of the dissolved NDMA precursors. However, other dissolved NDMA precursors are more recalcitrant. Extended biological treatment can effectively prevent NDMA formation by promoting nitrification and thus precluding chloramine formation during free chlorine addition. Otherwise, because recalcitrant tertiary amines are charged at circumneutral pH, they are effectively removed by reverse osmosis.; Other nitrosamines, many of which exhibit similar cancer potencies, are formed to a lesser degree. The formation of these other nitrosamines may be significant when the total cancer risk is assessed for exposure to N-nitrosamines in chloraminated wastewater. (Abstract shortened by UMI.)... |
